It has been determined that in automotive vehicles with internal combustion engines that have been adapted for use with alcohol fuels such as methanol or ethanol fuels, for instance in combination with gasoline, there are certain operating conditions in which conventional fueling of the engine at startup may be inadequate. Specifically, on hot restarts, when an engine is being restarted while hot from previous operation, fuel mixtures including alcohol at certain alcohol concentrations may be prone to extreme vaporization rates at the outlet of the fuel delivery means, which can interfere with proper engine fueling in a manner that is difficult to predict. Typically, such vaporization substantially decreases the amount of fuel made available to the engine which can lead to noticeable engine and catalytic converter operation instabilities.
Compensation for such hot restart fueling deficiencies is provided in the prior art. Known systems attempt to increase the pressure of the fuel in each of the fuel injectors, so as to suppress fuel vaporization at the outlet thereof. Additionally, known systems may attempt to supplement the amount of fuel supplied to the cylinders of the engine, such as by releasing stored fuel vapors into the engine intake air when vaporization is assumed to be taking place, Finally, prior art systems may simply decrease the desired air/fuel ratio to overcome the deficiencies.
Such systems, to be effective, must only compensate the fuel delivery system when needed, as they can have a deleterious effect on engine operation stability if they compensate when the fuel is not vaporizing rapidly. For instance, the engine air/fuel ratio can be driven to a rich condition in an unpredictable and undesirable manner by releasing fuel vapors to the engine, by increasing the pressure of the fuel supplied to the engine, or by increasing the desired air/fuel ratio when such compensation is not needed. Accordingly, a critical element in any approach to hot restart compensation is the capacity to predict accurately when such substantial vaporization will occur.
For a typical fuel delivery system, two conditions should normally be met before the fuel will vaporize at an extreme rate. First, the fuel, composed of conventional gasoline and a portion of either methanol or ethanol, must have an appropriate concentration of methanol or ethanol. There is a known concentration range wherein the fuel will be very volatile, meaning it will vaporize rapidly. Second, the temperature of the fuel delivery means, such as a conventional fuel injector, must be such that the volatile fuel passing through the injector will increase in temperature sufficiently to drive the vaporization rate to an extreme level.
If the injector is above a known threshold temperature, related to the pressure of the fuel in the injector and to the fuel concentration, extreme vaporization rates will normally take place due to extreme fuel volatility. For other concentrations and temperatures however, much less vaporization will likely occur, and additional compensation is not needed. Accordingly, the known prior art systems only compensate the fuel delivery means when the fuel is of a concentration and temperature that will rapidly vaporize at the pressure of the fuel delivery system.
Sensors are available to monitor the concentration of methanol or ethanol in vehicle fuel. However, in conventional systems using fuel injectors, it is difficult and expensive, due to severe packaging constraints, to provide accurate temperature sensors on the fuel injectors themselves. Systems are available in the prior art that check engine coolant temperature as a means of generally verifying that the engine is at a temperature at which vaporization is likely. For a more precise indication of injector temperature, these systems may monitor a fuel temperature sensor disposed in a fuel delivery conduit a distance upstream of the injector.
The difficulty with this fuel temperature sensor arrangement is the lack of a one-to-one mapping between a single sensor temperature and the actual injector temperature. In other words, a single fuel temperature sensor measurement in this arrangement may be indicative of more than one injector temperature. For example, a single sensor temperature may map to an injector temperature at which an extreme vaporization rate is normally possible, and to one at which such a rate is not normally possible. A system using such a mapping will, under certain conditions, provide compensation at times when it is not needed or, alternatively, fail to compensate when needed. Such improper targeting of compensation may exacerbate rather than reduce engine and converter instabilities, or may fail to address the instabilities altogether.
Accordingly, the prior art systems necessarily required the fuel temperature to exceed a very high threshold temperature before providing compensation, to reduce the risk of applying unnecessary compensation, as described. The coverage of such systems was thereby reduced in that the occasionally failed to predict extreme fuel vaporization rate conditions associated with lower sensed fuel temperature. Accordingly, the effectiveness of such prior art systems is limited.
What is needed is an economical method and apparatus for more accurately predicting when compensation is needed, by estimating when the injector temperature is such that, at the pressure and alcohol concentration of the fuel, the fuel will vaporize at an extremely high rate at the fuel delivery means.